Radiation absorbing polymer, composition for radiation absorbing coating, radiation absorbing coating and application thereof as anti-reflective coating

ABSTRACT

A radiation absorbing polymer having chemically bonded thereto a radiation absorbing dye, which has high absorption at a predetermined wavelength radiation, which shows good adhesion to a substrate and good thin film-forming, which has no dependence upon resists, which is soluble in a solvent for photoresists but becomes insoluble after being baked; a composition for radiation absorbing coating containing this polymer, and a radiation absorbing coating such as an anti-reflective coating formed from this composition are disclosed. The radiation absorbing polymer comprises a copolymer containing at least both a recurring unit composed of a monomer containing a keto group and a divalent group (preferably a methylene group) in its side chain and a recurring unit composed of a monomer containing an organic chromophore bonded directly or through a linkage group to the main chain. This radiation absorbing polymer is dissolved in a solvent such as alcohol, aromatic hydrocarbon, ketone, ester, etc., and the resulting solution is applied to a wafer and baked to form a radiation absorbing coating such as an anti-reflective coating. On this coating is coated, for example, a chemically amplified resist. This coated substrate is then exposed to deep UV rays and is developed to form a fine resist pattern excluding the influence of standing wave.

TECHNICAL FIELD

[0001] This invention relates to a radiation absorbing polymer which haschemically bonded thereto an organic chromophore, a coating compositioncontaining the radiation absorbing polymer and an anti-reflectivecoating formed from the coating composition and, more particularly, to aradiation absorbing polymer capable of forming a radiation absorbingcoating such as an anti-reflective coating useful in manufacturingintegrated circuit elements by lithography, a composition containing theradiation absorbing polymer, and a radiation absorbing coating such asan anti-reflective coating formed from the composition.

BACKGROUND ART

[0002] In the field of manufacturing integrated circuit elements,patterning technology to form finer patterns by lithographic process hasmade progress and, in recent years, in order to attain a higher degreeof integration, the development of patterning technology enablingquarter micron fine patterning has been studied. In such a lithographicprocess, a photoresist is applied to a substrate, a latent image of amask pattern is created in the photoresist using a reduction projectionexposure apparatus, then the latent image is developed using a properdeveloper solution to obtain a patterned resist with the desired widthand pattern. However, many substrates used in the field of manufacturingintegrated circuit elements have such a high reflectivity that, uponexposure, exposing light passing through the photoresist layer isreflected on the surface of the substrates and is again incident intothe photoresist layer, which causes the problem that desired patternsare not obtained or that patterns with some defects are formed due toexposure by the reflected light of photoresist areas which are not to beexposed. These are called problems of standing wave or notching. Varioustechniques have been investigated to solve the problems caused by suchreflection. For example, there have been attempted a technique ofdispersing a dye having radiation absorption at the same exposurewavelength as in the photoresist, a technique of forming a radiationabsorbing coating of an inorganic compound such as titanium nitrideaccording to a CVD method, vacuum evaporation method or the like, atechnique of forming a radiation absorbing coating by applying adispersion or solution of a radiation absorbing dye in an organicpolymer solution on to a substrate, and a technique of forming aradiation absorbing coating by applying to a substrate a radiationabsorbing polymer having chemically bonded thereto a chromophore. Of theabove-described techniques, the technique of dispersing a radiationabsorbing dye in a photoresist has the problems of reduction inphotoresist sensitivity, thinning of the resist layer during developmentprocessing, sublimation of the dye upon baking, and the like. Thetechnique of using an inorganic anti-reflective coating has the variousproblems of difficulty in accurate control of coating thickness,difficulty of forming a coating with uniform coating thickness,requirement for a special apparatus for conducting, vapor deposition,poor adhesion with a resist film, a requirement for separately providinga step of transferring a pattern by dry etching, and the like. Further,the technique of dispersing a radiation absorbing dye in theanti-reflective coating involves the problems of separation of thepolymer and the dye from each other upon formation of theanti-reflective coating by spin-coating, elution of the dye into aresist solvent, sublimation of the dye into the resist layer uponbaking, and the like. On the other hand, the technique of using aradiation absorbing polymer does not involve such problems, and hencethis technique has been noted in recent years. Methods of usingradiation absorbing polymers as anti-reflective coatings and materialsto be used for the methods are described in, for example, JapaneseLaid-open Patent Publication Nos. H6-75378 and H6-118656, WO 9412912,U.S. Pat. Nos. 4,910,122 and 5,057,399, etc. Of the radiation absorbingpolymers, those polymers wherein a radiation absorbing chromophore ischemically bonded to the polymer skeleton have recently been consideredmost promising, and methods of using them and their application, havealready been studied. Particularly in the process of using radiationhaving a wavelength not longer than that of an eximer laser, ananti-reflective coating is considered to be necessary, and it has beendesired to provide an anti-reflective coating having good properties.

[0003] On the other hand, there exists a requirement that, uponformation of a photoresist coating on a substrate having a largeunevenness, an undercoating layer or an intermediate layer is firstcoated on the substrate to make the surface even for forming a resistimage with high dimensional accuracy. Investigation for meeting such arequirement is also necessary.

[0004] Formation of resist patterns using a radiation absorbingintermediate coating such as an anti-reflective coating between aphotoresist layer and a substrate before forming a resist pattern isconducted as follows. That is, a composition for a radiation absorbingcoating such as an anti-reflective coating solution is first coated to asubstrate and, after baking the coating to be made insoluble in a resistsolvent, the resist coating is formed by a coating method on theradiation absorbing coating, such as the anti-reflective coating, and isthen subjected to the processes of exposure, development processing,etc. to form a resist pattern, followed by removing the coating such asthe anti-reflective coating in the resist-free areas, by dry etching orthe like.

[0005] The above-described radiation absorbing polymers wherein a dye ischemically bonded to a skeletal polymer, generally have a low solubilityin solvents for resists, and hence solvents different from those usedfor resists, such as cyclohexanone, are often employed as a solvent forthe radiation absorbing polymer. In case that a solvent used for forminga radiation absorbing coating, such as an anti-reflective coating, isdifferent from that for resist, there may arise problems that processsteps for forming the anti-reflective coating in manufacturingintegrated circuits increase in number and, in some cases, properties ofthe resist layer themselves are adversely affected. In addition, in thecase that the anti-reflective coating and the photoresist layer areformed by using the same coating apparatus and the anti-reflectivecoating materials are insoluble in the solvent for resist, there arisesa problem that the anti-reflective coating material might beprecipitated due to the influence of mixing of the resist coating wasteand the anti-reflective coating solution. The precipitate thus formedmight close up pipes for waste liquor, or might scatter as fine powder,resulting in pattern defects. Further, an additional pipe line forfeeding a solvent for washing the backside and periphery of substratemight be required. As is described above, an anti-reflective coatingcomposition containing a low molecular weight dye dispersed in a polymerhas also been developed. Such composition, however, often causesunevenness in coating thickness when coated on a surface of a substratewith topography, that is, it provides poor coverage, which shoulddesired to be improved. In addition, in conducting the resist process ona substrate with areas with topography, coating of the resist is, insome cases, difficult or it is difficult to make the thickness of theresist uniform, due to difference in the level of the surface. There isalso a requirement on planarization of the substrate surface by afilm-forming material to get uniform thickness of the resist coatingformed thereon for improving the accuracy of the formed resist pattern,as well as preventing reflection. Thus, it has been desired to providean anti-reflecting coating material which can provide high performance,which enables one to control coverage properties on a surface of asubstrate with topography, which undergoes no change in the propertiesof the anti-reflective coating upon baking, and which is soluble in asolvent for the resist.

[0006] Further, it has eagerly been required to attain higher resolutionin the resist process and, therefore, wavelength of radiation forexposing resists is being shifted to shorter wavelengths, and a processof using KrF laser (248 nm) has been put into practice. However, sincesubstrates presently used show high reflectivity for radiation of suchshort wavelength and since thickness of a resist is being reduced withthe enhancement of resolution, a radiation absorbing coating is desiredwhich can well prevent reflection even when used in a thin thickness inview of the dry etching process. Therefore, it is necessary to develop aradiation absorbing material which absorbs well the radiation of theshorter wavelength to be used, which shows no coating defects even whencoated in a thin thickness, and which can match with various kinds ofresists.

[0007] This invention is made to provide a radiation absorbing polymersatisfying these requirements, a composition containing such a radiationabsorbing polymer, and a radiation absorbing coating formed by using thecomposition.

[0008] That is, a first object of the present invention is to provide aradiation absorbing polymer which satisfies the above-described variousrequirements, that is, which shows high solubility in a resist solvent,which can form a radiation absorbing coating such as a conformalanti-reflective coating on a substrate with topography, which, in somecases, can fill up depressions on the surface of a substrate to make iteven, which shows a high anti-reflective effect, and which can form aresist pattern with good adhesion to the substrate and a resist layer,good dry etchability, high heat-resistance and excellent resolution.

[0009] A second object of this invention is to provide a compositionwhich can form a radiation absorbing coating capable of satisfying theabove-described requirements.

[0010] A third object of the present invention is to provide a methodfor forming a radiation absorbing coating capable of satisfying theabove-described requirements.

[0011] The other object of this invention is to provide a radiationabsorbing coating and an anti-reflective coating capable of satisfyingthe above-described requirements.

DISCLOSURE OF THE INVENTION

[0012] As a result of intensive investigations, the inventors have foundthat a radiation absorbing polymer satisfying the above-describedrequirements can be obtained by using a monomer having a keto group inits side chain as a recurring unit of the radiation absorbing polymer.

[0013] That is, one aspect of the present invention is a radiationabsorbing polymer which has absorption at a predetermined wavelengthradiation and which contains at least both a recurring unit having aketo group in its side chain and represented by the following generalformula (1) and a recurring unit having in its side chain an organicchromophore absorbing a predetermined wavelength radiation andrepresented by the following formula (2):

[0014] wherein R₁ and R₂-independently represent a hydrogen atom, analkyl group or other organic group, and R₃ represents an organic grouphaving at least one carbonyl group;

[0015] wherein R₄ and R₅ independently represent a hydrogen atom, analkyl group, a carboxyl group or other organic group, and Y represents agroup having an organic chromophore having an absorption at apredetermined wavelength radiation, said organic chromophore beingbonded directly or through a linkage group to the carbon atomconstituting the main chain.

[0016] Another aspect of the present invention is a composition forradiation absorbing coating containing the above-described radiationabsorbing polymer.

[0017] A further aspect of the present invention is a method of forminga radiation absorbing coating by applying the composition for radiationabsorbing coating on a substrate and baking it.

[0018] A still further aspect of the present invention is a radiationabsorbing coating and an anti-reflective coating formed according to theabove-described method.

[0019] The present invention is described in more detail by thefollowing descriptions which, however, should not be construed to limitthe scope of the present invention.

[0020] First, as is described above, the radiation absorbing polymer ofthe present invention is a radiation absorbing polymer containing atleast both the recurring unit represented by the formula (1) and therecurring unit represented by the formula (2) and absorbing at apredetermined wavelength of radiation. Preferred examples of therecurring unit represented by the formula 1 are those represented by thefollowing formula (3), (4) or (5). In the case that a plurality of ketogroups are in the recurring unit represented by the following formula(3), (4) or (5), the radiation absorbing polymer shows improvedsolubility in solvents usually used for resists, due to the existence ofthe keto groups and, in case that at least one hydrogen atom is bondedto the methylene group of the recurring unit, there results a hardcoating owing to the reaction with a cross linking agent based on theactivity of the hydrogen atom.

[0021] wherein R₁ and R₂ represent independently a hydrogen atom, analkyl group or other organic group, R₆ represents an organic groupcontaining at least one carbonyl group, X₁ represents O, S, NR₇ or astraight, branched or cyclic alkylene group containing at least onecarbon atom, R₇ represents a hydrogen atom or a substituted ornon-substituted, phenyl or cyclic,. straight or branched alkyl group.

[0022] wherein R₁, R₂, R₈, R₉ and R₁₀ represent independently a hydrogenatom, an alkyl group or other organic group.

[0023] wherein R₁, R₂/R₁₂, R₁₃ and R₁₄ represent independently ahydrogen atom, an alkyl group or other organic group, and R₁₁ representsa divalent group.

[0024] As monomers for constituting the recurring units represented bythe above-described formula 3 or 4, there are specifically illustratedthe following ones:

[0025] As the recurring unit represented by the above-described formula5, there are illustrated, for example, those wherein R₁₁ represents—OR₁₅O— or —NHR₁₅O— (wherein R₁₅ represents one of substituted ornon-substituted, straight, branched or cyclic alkylene groups or asubstituted or non-substituted phenylene group), with those wherein R₁₅represents an alkylene group such as an ethylene group. As monomers forconstituting the recurring units represented by the above-describedformula 3 or 5, there are specifically illustrated the following ones:

[0026] On the other hand, the recurring unit represented by the aboveformula 2 is more specifically exemplified by those represented by thefollowing formula 6 or 7:

[0027] wherein R₄ and R₅ represent independently a hydrogen atom, analkyl group, a carboxyl group or other organic group, and Ar is achromophore which absorbs the predetermined wavelength radiation andrepresents one of substituted or non-substituted benzene ring, condensedring or heterocyclic ring groups bonded directly or through a linkagegroup to the main chain carbon atom.

[0028] wherein R₄ and R₅ represent independently a hydrogen atom, analkyl group, a carboxyl group or other organic group, X₂ represents O,S, NR₁₆ or a straight, branched or cyclic alkylene group containing atleast one carbon atom, R₁₆ represents a hydrogen atom or a substitutedor non-substituted, phenyl group or cyclic, straight or branched alkylgroup and Ar₁ is a chromophore which has absorption at a predeterminedwavelength radiation and represents one of substituted ornon-substituted benzene ring, condensed ring or heterocyclic ring groupsbonded directly or through a linkage group to X₂.

[0029] Monomers used for constituting the recurring units represented bythe above formula 6 or 7 are exemplified by the following:

[0030] In addition, the radiation absorbing polymer of the presentinvention may contain other recurring units than those represented bythe formulae (1) and (2) in addition to the recurring units representedby the formulae (1) and (2) in order to impart the polymer highradiation absorbing property, high etching rate, good solubility for aparticular solvent, good storage stability, cross-linking property(curability) or other preferred properties. As monomers for constitutingsuch other recurring units, usually acrylates or methacrylates are usedfor imparting solubility to the resulting polymer, and styrenes are usedfor increasing Tg. Other specific examples of the other comonomers thanthose for constituting the recurring units of formulae 1 and 2, whichcan impart preferred properties, include methyl methacrylate, methylacrylate, 2-hydroxyethyl methacrylate, ethyl methacrylate,2-(methacryloyloxy) ethyl methacrylate, butyl methacrylate, t-butylmethacrylate, glycidyl methacrylate, methacrylic acid, acrylic acid,acrylonitrile, acrylamide, hydroxymethylacrylamide, 2-isocyanatoethylmethacrylate, 4-acetoxystyrene, 3-methyl-4-hydroxystyrene, styrene,vinyl chloride, ethyl vinyl ether, butyl vinyl ether, isobutyl vinylether, cyclohexyl vinyl ether, methyl vinyl ether, maleic anhydride,maleimide, N-substituted maleimide, vinyl acetate, 2-isocyanatoethylacrylate, etc. Of these, methyl methacrylate, methacrylic acid, methylacrylate, 2-hydroxyethyl methacrylate, hydroxymethylacrylamide, butylmethacrylate, t-butyl methacrylate, glycidyl methacrylate, methyl vinylether, butyl vinyl ether, etc. are preferred.

[0031] Main properties to be imparted by these comonomers areillustrated below. In the case of using together with organicchromophore, radiation absorption is more enhanced by using, forexample, 2-isocyanatoethyl acrylate, maleic anhydride, maleimide,N-substituted maleimide, 2-isocyanatoethyl methacrylate, etc. as thecomonomers, etching rate is increased by using, for example, methylmethacrylate, methyl acrylate, 2-hydroxyethyl methacrylate, ethylmethacrylate, butyl methacrylate, t-butyl methacrylate, acrylic acid,vinyl chloride, etc., solubility for solvents commonly used as solventsfor photoresists such as propylene glycol monomethyl ether acetate(PGMEA) or ethyl lactate is improved by using, for example,2-(methacryloyloxy)ethyl methacrylate, acrylic acid, 4-acetoxystyrene,3-methyl-4-hydroxystyrene, ethyl vinyl ether, butylvinyl ether, isobutylvinyl ether, cyclohexylvinyl ether, methyl vinyl ether, vinyl acetate,etc., cross-linking property (curability) is improved by using, forexample, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate,methacrylic acid, glycidyl methacrylate, hydroxymethylacrylamide, etc.,Tg is increased by using, for example, styrene,3-methyl-4-hydroxystyrene, etc. However, the above-described specificcomonomers and properties imparted by them are to be construed as merelyillustrative and not limitative at all.

[0032] As the monomers constituting the recurring unit having in theside chain thereof an organic chromophore which absorbs a predeterminedwavelength radiation, there are illustrated, for example, those whereina hydroxyl group- or amino group-containing organic chromophore ischemically bonded to the acid anhydride group or a carboxyl group bondedto the main chain.

[0033] Molecular weight and proportion of the recurring units of theradiation absorbing polymer in accordance with the present invention canwidely be varied but, in the case of using as a material for formingradiation absorbing coating, those which have a molecular weight of fromabout 1,000 to about 500,000 and contain at least 5 mol %, based on thewhole recurring units, of the recurring unit represented by the formula1 and at least 10 mol % of the recurring unit represented by the formula2 are preferred. More preferably, each of the recurring unitsrepresented by the formulae 1 and 2 are contained in an amount of 15 mol% or more based on the whole recurring units.

[0034] The radiation absorbing polymer of the present invention can beused as, for example, a material for bottom anti-reflective coating usedin manufacturing integrated circuits by dissolving the polymer in asolvent. In the case of employing ultraviolet or deep ultraviolet ray asan exposure source for manufacturing integrated circuits using theradiation absorbing polymer of the present invention, the polymerpreferably has a strong absorption in the wavelength region of from 180to 450 nm. In order to obtain such a radiation absorbing polymer, properrecurring unit or units are selected from the recurring unitsrepresented by the foregoing formula (2) and, if necessary, from therecurring units represented by the formula (1) or from the recurringunits other than those represented by the formulae (1) and (2). Use ofsuch properly selected recurring units represented by the formula (2),capable of strongly absorbing radiation of the exposure wavelength,enables the radiation absorbing polymer containing the recurring unitsto strongly absorb the radiation used for exposure, thereby reflectionof the exposure radiation from the substrate is prevented and adefect-free resist pattern is formed.

[0035] The composition for radiation absorbing coating of the presentinvention contains the above-described radiation absorbing polymer andcomprises the radiation absorbing polymer and, if necessary, additivesdissolved in a proper solvent. As the solvent to be used for thecomposition of the present invention, any of those that haveconventionally been used for forming a coating and can dissolve theradiation absorbing polymer and other additives may be used. Aspreferred examples of the solvents, there are illustratedγ-butyrolactone, cyclohexanone, dimethylacetamide, dimethylformamide,dimethylsulfoxide, N-methylpyrrolidone, ethyl lactate (EL), methoxypropanol (PGME), propylene glycol monomethyl ether acetate (PGMEA),methyl amyl ketone (MAK) or an optional mixture thereof. Of these,γ-butyrolactone, cyclohexanone, EL, PGME, PGMEA and a mixed solvent ofPGME and PGMEA are particularly preferable solvents.

[0036] Concentration of the radiation absorbing polymer in thecomposition can be varied over a wide range depending upon the purposeof use of the composition and the thickness of the radiation absorbingcoating. For example, in the case of use as an anti-reflective coating,it is usually 20% by weight or less

[0037] As the additives to be contained in the composition for radiationabsorbing coating of the present invention, there are illustrated, forexample, conventionally known radiation absorbing compounds, surfactantsor silane series leveling agents for improving adhesion to a substrateand enhancing coating properties, and the like. In addition, in order toenhance cross-linking density upon formation of the coating, commonlyknown cross-linking agents and cross-linking auxiliaries may be added.As cross-linking agents and cross-linking auxiliaries, there arespecifically illustrated melamine compounds, substituted urea compounds,acid-generating agents which can generate acid upon being heated orirradiated to thereby accelerate cross linking, bisblocked isocyanates,blocked isocyanates and epoxy group-containing polymers, etc. Thesecross-linking agents or auxiliaries may be either low molecular weightcompounds or polymers. These cross-linking agents or auxiliaries aredesirably added in an amount of 0.1 to 50% by weight based on the weightof the radiation absorbing polymer. In the composition for radiationabsorbing coating may also be incorporated, if necessary, low molecularweight compounds or polymers other than the polymer of the presentinvention.

[0038] The radiation absorbing coating of the present inventioncontaining the radiation absorbing polymer may be formed on, forexample, a substrate by coating on a substrate a composition forradiation absorbing coating obtained by dissolving the radiationabsorbing polymer and, if necessary, desired additives in a propersolvent or, in some cases, by conducting the polymer-forming reaction onthe substrate to thereby directly form a coating of the reaction producton the substrate.

[0039] The radiation absorbing coating composition is coated on asubstrate in a proper thickness depending upon its use. In the case offorming, for example, an anti-reflective coating, it is coated on asubstrate in a dry thickness of 300 to 5,000 Å, by spin coating, castcoating, roller coating or the like. After the coating procedure, thecoating is baked on a hot plate or in an oven to make it insoluble in aresist solvent. The baking is conducted at a temperature of about 90 to260° C., preferably 160° C. or above.

[0040] A photoresist is applied to the radiation absorbing coating, suchas the anti-reflective coating thus formed on the substrate, in apredetermined thickness, then prebaked to form a photoresist layer. Asthe photoresist, either positive working or negative workingphotoresists can be used. Typical examples of usable photoresistsinclude a positive working photoresist comprising novolak resin and aquinonediazide type light-sensitive agent, a chemically amplifiedresist, etc. which, however, are not limitative at all. Solvents for thephotoresist include EL, PGME, PGMEA, ketones, etc. Prebakingtemperatures vary depending upon the kind of photoresist to be used, butis usually about 30 to about 200° C. The radiation for exposure of thephotoresist can be selected from among visible light, UV rays, deep UVrays, KrF eximer laser, argon fluoride (ArF) laser (193 nm), X-rays,electron beams, etc. As the radiation absorbing polymer used inradiation absorbing coating to prevent the reflection from thesubstrate, those polymers which absorb the radiation of wavelengthsrequired for exposure, as has been described hereinbefore, are selected.After exposure, the photoresist is subjected to development with adeveloper solution after optionally post-exposure baking, a resistpattern thus being formed. The radiation absorbing coating such as theanti-reflective coating is then dry etched using gas plasma such asoxygen plasma to thereby form a defect-free resist pattern that servesto process or treat the substrate. Additionally, as the developersolution, there may be used known developers such as an alkaline aqueoussolution which contains a metal hydroxide, an organic amine or the likedissolved therein.

[0041] By selecting the processing conditions, the composition forradiation absorbing coating of the present invention may also be used asa coating which functions to prevent reflection of radiation and toprevent adverse mutual action between the substrate and the resist or toprevent the adverse action of materials used in the resist or substancesproduced upon exposure of the resist on the substrate. Further, it maybe used as a coating for planarizing the surface of the substrate onwhich a pattern has already been formed (substrate having topography) byfill up depressions on the surface before coating a photoresist thereonto thereby enhance uniformity in the thickness of the coating, such as aphotoresist to be coated thereon.

[0042] Additionally, in the case of using the radiation absorbingcoating of the present invention as a coating which planarizes thesubstrate surface, it is proposed to slightly reduce the glasstransition temperature (Tg) of the radiation absorbing polymer to causesome flow upon baking and, after being completely solidified, make thecoating insoluble in resist solvents. The slight reduction in Tg may beattained, for example, by slightly reducing the cross-linking ability ofthe radiation absorbing polymer upon being heated. In order to impart tothe polymer the function flat XXXX the surface of the substrate, thereare various techniques of, for example, properly selecting this degreeof polymerization of the radiation absorbing polymer, concentration ofthe radiation absorbing polymer in the composition or substituents inthe recurring units represented by the formula (1) or (2) and properlyselecting the proportion of the recurring units represented by theformulae (1) and (2) in the polymer and a type of comonomer other thanthose represented by the formula (1) or (2), or properly selecting thetype of additives.

[0043] The coating composition for radiation absorbing of the presentinvention is soluble in a solvent for a photoresist. Therefore, itenables one to use the same coating apparatus, the same waste liquorapparatus and the same rinsing solution as those used for the resist. Inaddition, the anti-reflective coating using the radiation absorbingpolymer of the present invention which shows a high absorption of DUV(248 nm) can preferably be used as an anti-reflective coating forchemically amplified resists sensitive to DUV. Further, the radiationabsorbing coating of the present invention has such a low dependenceupon resists that anti-reflective coating materials are not required tobe changed when resists are changed in the manufacture of IC, andtherefore, no process changes have to be evalusted, which is extremelyadvantageous for users. For example, AZ®-BARLi® coating manufactured byClariant Corp . . . , a commercially available anti-reflective coatingmaterial, designed for i-line (365 nm) exposure is very soluble incyclohexanone, but is barely soluble in a resist solvent and has,therefore, the defect that used the same coating apparatus as that forcoating resist is difficultly used upon applying the anti-reflectivecoating composition or upon edge rinsing. In addition, though AZ®-BARLi®coating itself absorbs DUV, it has such a resist dependence that, insome cases, footing or undercut is observed in the profile of aresulting resist pattern. The radiation absorbing polymer of the presentinvention also has the feature that, while it is soluble in a resistsolvent, it forms a film insoluble in the resist solvent and, is also,insoluble in an aqueous alkaline developer solution for resists, due tobeing heated at a proper temperature after coating on a substrate.Therefore, the radiation absorbing coating such as the anti-reflectivecoating of the present invention never suffers dissolution when aphotoresist coating composition Is coated thereon or when wet adevelopment processing is conducted after exposure. Still further, theradiation absorbing coating of the present invention has the featurethat, when a resist pattern is used as an etching mask, it can easily beremoved by dry etching.

[0044] Additionally, the radiation absorbing polymer of the presentinvention may be obtained according to various known synthesizingprocesses. For example, there is illustrated a process of copolymerizinga monomer having a keto group in the side chain and corresponding to therecurring unit represented by the foregoing formula (1) with a monomerhaving an organic chromophore and corresponding to the recurring unitrepresented by the foregoing formula (2). The monomer having an organicchromophore may easily be obtained by known synthesis processes, forexample, by converting a hydroxyl group- or amino group-containingorganic chromophore compound to its acrylate or acrylamide. As theprocess for obtaining the radiation absorbing polymer, theabove-described copolymerization process is the most popular. However,it is also possible to introduce a radiation absorbing group into apolymer by the reaction between a polymer having a reactive group and anorganic chromophore compound having a hydroxyl group, an amino group, orthe like.

[0045] In the present invention, polymerization may be conducted in aproper solvent using a free radical or ionic reaction initiator. Theresulting copolymer may be of various structures such as a randomcopolymer or a block copolymer. As preferred solvents for thepolymerization, there are illustrated toluene, tetrahydrofuran, benzene,dimethylformamide, dimethylsulfoxide, ethyl lactate, propylene glycolmonomethyl-ether acetate (PGMEA), cyclopentanone, cyclohexanone,butyrolactone, 2-heptanone, ethyl-3-ethoxypropanate, ethylene glycolmonoethyl acetate, methyl-3-methoxypropanate, etc. These solvents may beused alone or in combination of two or more of them.

[0046] As specific examples of the reaction initiators, there areillustrated 2,2′-azobis(isobutyronitrile)(AIBN), 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis(2-cyclopropylpropionitrile), 2,2′-azobis(2,4-dimethyl valeronitrile),2,2′-azobis(2,4-dimethylpentanenitrile),1,1′-azobis(cyclohexanecarbonitrile), benzoyl peroxide, t-butyl peroxybenzoate, di-t-butyl diperoxy phthalate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxy pivalate, t-amyl peroxy pivalate, butyllithium, etc. However, initiators are not limited only to these.

[0047] These polymers may be separated from the solvent, then againdissolved in a proper solvent to prepare an anti-reflective coatingcomposition or a composition for radiation absorbing coating or, if thesolvent used in the synthesis reaction can be utilized as a solvent forthe anti-reflection coating composition or composition for radiationabsorbing coating, it may directly be used as the anti-reflectivecoating composition or composition for radiation absorbing coatingwithout separating the polymer, or the reaction solution may directly beapplied to a substrate such as a wafer after completion of the reaction.Additionally, the anti-reflective coating composition or composition forradiation absorbing coating is desirably subjected to filtration using,for example, using a 0.5, 0.2 or 0.1 micron (μm) filter to therebyremove insoluble fine particles. The filtered solution may directly beapplied to a substrate such as a wafer.

[0048] Molecular weight of the thus obtained polymer varies dependingupon polymerization time, reaction temperature, concentrations of usedmonomers and initiators, kind of reaction medium, etc. and can easily becontrolled by properly selecting these parameters. Polymers having anarrow molecular weight distribution may be obtained by employing ionicpolymerization.

[0049] Molar ration of the comonomers in the radiation absorbing polymeris decided based on reaction rate of each monomer and employed reactionconditions. The radiation absorption and refractive index of finalpolymer to a desired wavelength radiation is quite important indetermining whether the polymer can be used as a bottom anti-reflectivecoating or the like or not. Radiation absorption of the coating ispreferably in the range of from 2 to 40 per micron in thickness, with 5to 25 being more preferred. Copolymers composed of three or more typesof comonomers also required to provide such absorption. Too strong ortoo weak absorption fails to provide favorable results as ananti-reflective coating. Radiation absorbing properties required foranti-reflective coating materials also depend upon radiation absorbingproperties and refractive index of the photoresist material to be coatedthereon. Most preferably, the refractive index of the anti-reflectivecoating is the same as that of the photoresist layer to be coatedthereon and, if not, the two indexes are preferably as close as possibleto each other. Since radiation absorbing properties of theanti-reflective coating materials are determined by the radiationabsorbing properties and molar ratio of the chromophore-containingmonomer, the proportion of the chromophore-containing monomer in mol %is important for the anti-reflective coating material. In the presentinvention, this proportion can easily be controlled by adjusting thecharging proportion of the chromophore-containing monomer, and a polymerwith the desired values can be prepared.

BEST MODE FOR PRACTICING THE INVENTION

[0050] The present invention is now described in more details byreference to the following Examples. These examples, however, are onlyillustrative to explain the present invention and are not intended tolimit the scope of the present invention.

Synthesis Example 1 Synthesis of 9-Methacryloyloxymethylanthracene

[0051] 87.5 g (0.42 mol) of 9-hydroxymethylanthracene was added to 500ml of ethyl acetate at room temperature. To this was further added 7.3 g(60 millimols) of 4-dimethylaminopyridine under stirring, and 83 g (0.54mol) of methacrylic anhydride was dropwise added thereto. Thereafter,the reaction mixture solution was stirred at 60° C. for about 4 hoursuntil the reaction was completed. After completion of the reaction, thereaction product was cooled to room temperature, and ethyl acetate wasadded thereto. The organic layer was washed with, successively, analkaline water and water, then subjected to distillation under reducedpressure to remove the organic solvent and obtain a solid end product.Yield was 80 g (73 %) . This product was identified by measurement ofthe UV absorption in methanol and NMR. The UV absorption measurementrevealed that the molar extinction coefficient at 248 nm was 1.05×10⁵.¹H-NMR(DMSO-d6), (400 MHz) measurement showed signals at 1.82(s,3H),5.59(s,1H), 5.9(s,1H), 6.2(s,2H), 7.49-7.7(m,4H), 8.12(m,2H), 8.4(m,2H)and 8.67(s,1H).

Synthesis Example 2 Synthesis of 1-Methacryloylaminoanthracene

[0052] 25 g (0.13 mol) of 1-aminoanthracene was dissolved in 120 ml ofethyl acetate at room temperature. To this solution was added 0.61 g (5millimols) of 4-dimethylaminopyridine and, under stirring, a mixedsolution of 24.6 g (0.16 mol) of methacrylic acid anhydride and 30 ml ofethyl acetate was added dropwise thereto over about 5 minutes.Thereafter, the reaction mixture solution was stirred at 50° C. for 3hours, then cooled to room temperature, followed by collecting theprecipitate formed by filtration. The precipitate was washed twice withethyl acetate, then dried under vacuum to obtain the end product of1-methacryloylaminoanthracene. Yield was 18.6 g (60% ). Further, about 9g of the end product was obtained from the filtrate. Measurement of theU absorption in methanol revealed that molar extinction coefficient at248 nm was 4.1×10⁴ .

Example 1

[0053] 55.2 g (0.2 mol) of 9-methacryloyloxymethylanthracene and 42.8 g(0.2 mol) of acetylacetoxyethyl methacrylate were dissolved in 500 ml oftetrahydrofuran (THF), and 3.28 g (20 millimols) ofazobisisobutyronitrile (AIBN) was added thereto as a radical initiator.Then, the mixture was stirred at room temperature for 15 minutes whileintroducing thereinto nitrogen, followed by heating the reaction mixturesolution at a reflux temperature for 10 hours. Thereafter, the reactionsolution was cooled to room temperature, then poured into isopropanol(IPA) to form a precipitate. The precipitate was collected byfiltration, washed with IPA, and dried in vacuo at 50° C. to obtain apolymer (hereinafter referred to as “polymer A”) . Yield was 78 g (82%). ¹H-NMR(DMSO-d6) measurement revealed the presence of a proton on thearomatic ring or anthracene (6.5-8.3 ppm) and a methylene proton boundto anthracene (5.2-6.3 ppm). Further, the integral ratio of proton ofethyl derived from acetylacetoxyethyl methacrylate (—OCH₂CH₂O—, 3-4 ppm)revealed that the molar ratio of 9-methacryloyloxymethylanthracenemonomer to acetylacetoxyethyl methacrylate in the polymer was about1.06:1. GPC analysis using dimethylformamide as a mobile phase andpolyethylene oxide as a standard substance revealed that polymer A had aweight average molecular weight, Mw, of 17,000, a number averagemolecular weight, Mn, of 8,430, and degree of dispersion, Mw/Mn, of2.03. Separately, polymer A was dissolved in PGMEA in a concentrationcapable of being coated on a silicon wafer in a thickness of about 100nm by spin coating, coated on a silicon wafer, and baked at 200° C. for60 seconds. The optical absorption coefficient (k value) at 248 nm ofthe thus formed coating was measured as 0.58, using a spectralellipsometer. When polymer A was mixed with PGMEA in a proportion of 10wt % and stirred at room temperature, the polymer was completelydissolved.

Example 2

[0054] Polymers were synthesized in the same manner as in Example 1except for changing charging the ratio of9-methacryloyloxymethylanthracene (MAOMA) and acetylacetoxyethylmethacrylate (AAEM) to the values described in synthesis numbers 1 and 2shown in Table 1. Copolymerization ratios (molar ratio) of MAOMA to AAEMof the thus obtained polymers were measured and confirmed. The opticalabsorption coefficients k of the polymer coating at 248 nm were measuredusing a spectral ellipsometer. Results of the measurements are shown inTable 1. Further, elution tests revealed that every polymer was readilysoluble in a resist solvent such as PGMEA. From these results, it isseen that the present invention can provide polymers showing a highabsorption and being soluble in a resist solvent with a goodreproducibility. TABLE 1 molar ratio in molar ratio of polymer based onmonomer NMR spectrum value of k Synthesis No. MAOMA:AAEM MAOMA:AAEM (248nm) 1 0.5:1 0.55:1 0.48 2 0.6:1  0.5:1 0.51 3-1   1:1 1.06:1 0.58(Example 1) 3-2   1:1  1.1:1 0.59 (repeat of Example 1)

Example 3

[0055] 52.2 g (0.2 mol) of 1-methacryloylaminoanthracene and 42.8 g (0.2mol) of acetylacetoxyethyl methacrylate were dissolved in 500 ml oftetrahydrofuran (THF) at room temperature, and 3.28 g (20 millimols) ofazobisisobutyronitrile (AIBN) was added thereto as a radical initiator.Then, the mixture was stirred at room temperature for 15 minutes whileintroducing thereinto nitrogen, followed by heating the reaction mixturesolution at a reflux temperature for 10 hours. Thereafter, the reactionsolution was cooled to room temperature, then poured into isopropanol(IPA) to form a precipitate. The precipitate was collected byfiltration, washed with IPA, and dried in vacuo at 50° C. to obtain apolymer. Yield was 82 g (89%) . The integral ratio of proton in theanthracene moiety to proton of ethyl derived from acetylacetoxyethylmethacrylate (—OCH₂CH₂O—) by ¹H-NMR(DMSO-d6) measurement revealed thatthe molar ratio of the two monomers in the polymer was about 1:1. GPCanalysis using dimethylformamide as a mobile phase and polyethyleneoxide as a standard substance revealed that the obtained polymer had aweight average molecular weight, Mw, of 35,000, a number averagemolecular weight, Mn, of 15,200, and degree of dispersion, Mw/Mn, of2.3. Separately, this polymer was formed into a coating by baking at200° C. for 60 seconds. The optical absorption coefficient, k at 248 nmof the thus formed coating was measured as 0.4 using a spectralellipsometer.

Example 4

[0056] 41.4 g (0.15 mol) of MAOMA, 32.1 g (0.15 mol) of AAEM and 15 g(0.15 mol) of methyl methacrylate were dissolved in 500 ml oftetrahydrofuran (THF) at room temperature, and 3.28 g (20 millimols) ofazobisisobutyronitrile (AIBN) was added thereto as a radical initiator.Then, the mixture was stirred at room temperature for 15 minutes whileintroducing thereinto nitrogen, followed by heating the reaction mixturesolution at a reflux temperature for 10 hours. Thereafter, the reactionsolution was cooled to room temperature, then poured into isopropanol(IPA) to form a precipitate. The precipitate was collected byfiltration, washed with IPA, and dried in vacuo at 50° C. to obtain apolymer (hereinafter referred to as “polymer B”) . Yield was 68.8 g(80%) . GPC analysis using dimethylformamide as a mobile phase andpolyethylene oxide as a standard substance revealed that the obtainedpolymer had a weight average molecular weight, Mw, of 30,000, a numberaverage molecular weight, Mn, of 14,300, and degree of dispersion,Mw/Mn, of 2.1. Separately, this polymer was formed into a coating bybaking at 200° C. for 60 seconds. The optical absorption coefficient kat 248 nm of the thus formed coating was measured as 0.53 using aspectral ellipsometer. Results of elution test showed that the polymerhad a high solubility in resist solvents such as PGMEA,PGME and EL.

Example 5 Preparation of Radiation Absorbing Composition

[0057] 6 g of the polymer A obtained in Example 1 was dissolved in 100 gof PGMEA at room temperature with stirring and, after the polymer wascompletely dissolved, this solution was filtered through a 0.1-micronfilter to obtain composition C for radiation absorbing coating.Separately, in this composition C for radiation absorbing coating weredissolved hexamethoxymethylmelamine (20 wt % based on polymer A) and2,4-bistrichloromethyl-6-styryl-s-triazine (2 wt % based on polymer A),and the resulting solution was filtered through a 0.1-micron filter toobtain composition D for radiation absorbing coating.

[0058] Further, 5 g of polymer B obtained in Example 4 was dissolved in100 g of PGMEA at room temperature with stirring, and this solution wasmixed with 15 wt % based on the polymer of CORONATE® 2507 (blockedbisisocyanate; manufactured by Nippon Polyurethane K.K.) and, afterstirring for a while, the mixture was filtered through a 0.1-micronfilter to obtain composition E for radiation absorbing coating.

Comparative Example 1

[0059] AZ®-BARLi® solution for forming an anti-reflective coating soldby Clariant Corp. was coated on to a 4-inch silicon wafer by spincoating under proper conditions. The thus obtained sample was used forthe following experiments for comparison.

Example 6

[0060] The compositions C, D and E for radiation absorbing coatingprepared in Example 5 were respectively spin coated on to a 4-inchsilicon wafers under proper conditions. The thus obtained samples wereused in the following experiments for comparison.

Example 7 Experiment for Comparing Rinsing Property Before Baking

[0061] The rinsing properties of the radiation absorbing coating wereexamined by dropping a rinsing solution (PGME:PCMEA=70:30 (by weight))for 10 seconds, 20 seconds or 30 seconds onto a non-baked compositionfor radiation absorbing coating placed on a silicon wafer on a spincoater rotating at 800 rpm. As a result, it was found that radiationabsorbing coatings formed from the compositions C, D and E for radiationabsorbing coating of the present invention were completely removed bythe 10-second rinsing, whereas a comparative film of AZ®-BARLi® coatingprepared by a comparative examination 1 was removed only partly evenwith a 30-second rinsing.

Example 8 Experiments for Comparing Coverage

[0062] A resist pattern was previously formed on a silicon wafer, bakedat a high temperature of about 250° C. to make the resist patterninsoluble in a resist solvent, and platinum was vapor deposited thereonto prevent adverse mutual action between the resist pattern and thecomposition for radiation absorbing coating and to facilitateobservation under a scanning electron microscope (SEM). Thereafter, eachof the compositions C, D and E for radiation absorbing coating preparedin Example 5 was coated onto the silicon wafer having a difference insurface level. On the other hand, AZ®-BARLi® coating manufactured byClariant Corp. was similarly coated for comparison. These samples werebaked on a hot plate at 100° C. for 90 seconds, then cross sections ofthe patterns were observed under the scanning electron microscope (SEM). As a result, it was found that films obtained from the radiationabsorbing polymers of the present invention were formed along thepattern form, thus showing the same coverage property as AZ®-BARLi®film.

[0063] It was also found that some of the compositions for radiationabsorbing coating obtained from polymers having Tg value lowered bychanging the monomer ratio can be coated and fill the depressions of thepatterned surface, by baking at a proper temperature of, for example,lower than the cross linking temperature to fluidize the polymer layer,then raising the baking temperature so as to cross link the polymer.Such coating can generally be used as a leveling coating.

Example 9 Experiment of Dissolution of Baked Anti-reflective CoatingInto a Resist Solvent

[0064] The composition E for radiation absorbing coating of the presentinvention was coated onto a silicon wafer at a in dry thickness of1000Å, and was baked at a temperature of 180° C. , 200° C. or 220° C. Aresist solvent of EL, PGMEA or MAK was dropped onto the baked coatingsand, after two minutes, the dropped solvent was wiped off to measure theamount of coating removed. Results thus obtained are shown in Table 2.It is seen from the results shown in Table 2 that the radiationabsorbing coating of the present invention formed by using the radiationabsorbing polymer soluble in the resist solvents and baking at asuitable temperature does not undergo change of the coating itself, suchas being dissolved in a resist composition, when a photoresist is formedthereon. In addition, when a developer solution (2.38 wt % aqueoussolution of tetramethylammonium hydroxide) was dropped onto each of thecoatings to measure the amount of removed coating in the same manner asdescribed above, there were obtained similarly excellent results. TABLE2 Baking temperature 180° C. 200° C. 220° C. E L 570 Å 70 Å  5 Å PGMEA1050 Å  60 Å −1 Å MAK 670 Å 35 Å −1 Å

Example 10 Experiments of Testing Resist Pattern

[0065] Each of the radiation coating compositions D and E of the presentinvention was coated onto a silicon wafer at a dry thickness of about600 Å, and baked at 220° C. for 60 seconds to form anti-reflectivecoatings. Then, AZ® DX1100P, resist for DUV manufactured by ClariantJapan. was coated thereon in a thickness of 0.75 micron, patternwiseexposed and developed under predetermined conditions to form a resistpattern on each of the anti-reflective coatings. For comparison, aresist pattern was formed in the same manner on an anti-reflectivecoating composed of AZ®-BARLi® coating at a in thickness of 1200 Å.Observation of the cross section of each of the thus obtained resistpatterns under SEM revealed that the resist patterns formed by using theanti-reflective coatings of the present invention had higher resolutionthan that of AZ®-BARLi® film, no footing and no undercut. On the otherhand, the resist pattern formed by using AZ®-BARLi® coating showedfooting. The footing phenomenon may be attributed to adverse mutualaction between an acid generated in the exposed areas and the AZ®-BARLi®anti-reflective coating.

[0066] Pattern tests conducted by using other DUV photoresists on thereflective coatings of the present invention demonstrated good results.

Example 11 Experiment of Comparing Etchability

[0067] Anti-reflective coating films obtained from the radiationabsorbing composition of the present invention and an anti-reflectivecoating film obtained from AZ®-BARLi® coating were formed in the samethickness from each other, baked at 220° C., and subjected to an etchingtest using a dry etching apparatus. As a result of comparing the etchrate of each coating film, it was found that the polymer films of thepresent invention were etched at about the same etching rate as theAZ®-BARLi® film, with some of the polymer films of the present inventionbeing etched at somewhat faster rate than the film of AZ®-BARLi® film.

Effect of the Invention

[0068] As has been described hereinbefore, the radiation absorbingpolymer of the present invention which contains a dye moiety having anabsorption at a proper wavelength shows a good radiation absorption fora radiation of the wavelength, enables one to form an anti-reflectivecoating with a good adhesion and, since it is soluble in a solvent to beused as a resist solvent, the same coating apparatus, the same wasteliquor apparatus, and the same rinsing solution can be used as those forphotoresists in practicing the resist process, thus unnecessaryprocesses or equipment being eliminated.

[0069] In addition, the radiation absorbing polymer of the presentinvention can easily be formed into a film, and can be made insoluble inresist solvents by heating at a proper temperature after being coated.Hence, it enables one to form a radiation absorbing coating such as ananti-reflective coating which is not dissolved in a resist compositionor a developer solution for resist during formation of a photoresistlayer or during development processing and which can be easily removedby dry etching, thus being well adapted for the resist process.

[0070] Further, in the case of coating the composition for radiationabsorbing coating of the present invention on a substrate withtopography, the composition shows such good coverage that a mask patternwith high resolution can be formed on the substrate with topography.Still further, in the resist process, it is sometimes required toimprove the process latitude of the resist by planarization of asubstrate. The composition for radiation absorbing coating of thepresent invention can level the uneven surface using copolymers obtainedby properly adjusting the copolymerization ratio of copolymers,selection of the kinds of comonomer, constitution, baking temperature,etc., thus being capable of finding a wide application.

[0071] Still further, even in the case of using DUV photoresists posingsevere requirements on a substrate, the anti-reflective coating can beused as one for plural DUV photoresists due to the low dependence of theradiation absorbing coating of the present invention.

Industrial Applicability

[0072] As has been described hereinbefore, the radiation absorbingpolymer and the composition for radiation absorbing coating of thepresent invention are preferably used as a material for forming aradiation absorbing coating, particularly an anti-reflective coating, inmanufacturing integrated circuit elements.

1. A radiation absorbing polymer which absorbs a predeterminedwavelength radiation and which contains at least both a recurring unitrepresented by the following formula 1 and a recurring unit representedby the following formula 2:

wherein R₁ and R₂ independently represent a hydrogen atom, an alkylgroup or other organic group, and R₃ represents an organic group havingat least one carbonyl group;

wherein R₄ and R₅ independently represent a hydrogen atom, an alkylgroup, a carboxyl group or other organic group, and y represents a grouphaving an organic chromophore having an absorption at a predeterminedwavelength radiation, said organic chromophore being bonded directly orthrough a linkage group to the carbon atom constituting the main chain.2. The radiation absorbing polymer described in claim 1 which absorbs apredetermined wavelength radiation, wherein said recurring unitrepresented by the formula 1 is a recurring unit represented by thefollowing formula 3:

wherein R₁ and R₂ represent independently a hydrogen atom, an alkylgroup or other organic group, R₆ represents an organic group containingat least one carbonyl group, X₁ represents O, S, NR₇ or a straight,branched or cyclic alkylene group containing at least one carbon atom,R₇ represents a hydrogen atom or a substituted or non-substituted,phenyl group or cyclic, straight or branched alkyl group.
 3. Theradiation absorbing polymer described in claim 1 which absorbs apredetermined wavelength radiation, wherein said recurring unitrepresented by the formula 1 is a recurring unit represented by thefollowing formula 4:

wherein R₁, R₂, R₈, R₉ and R₁₀ represent independently a hydrogen atom,an alkyl group or other organic group.
 4. The radiation absorbingpolymer described in claim 1 which absorbs a predetermined wavelengthradiation, wherein said recurring unit represented by the formula 1 is arecurring unit represented by the following formula 5:

wherein R₁, R₂ R₁₂, R₁₃ and R₁₄ represent independently a hydrogen atom,an alkyl group or other organic group, and R₁ represents a divalentgroup. 5.The radiation absorbing polymer described in claim 4 whichabsorbs a predetermined wavelength radiation, wherein R₁₁ in formura 5represents —OR₁₅O-group (wherein R₁₅ represents one of substituted ornon-substituted, straight, branched or cyclic alkylene groups or asubstituted or non-substituted phenylene group).
 6. The radiationabsorbing polymer described in claim 5 which absorbs a predeterminedwavelength radiation, wherein R₁₅ represents an ethylene group.
 7. Theradiation absorbing polymer described in claim 4 which absorbs apredetermined wavelength radiation, wherein R₁₁ in formula 5 represents—NHR₅O— group(wherein R₁₅ represents one of substituted ornon-substituted, straight, branched or cyclic alkylene groups or asubstituted or non-substituted phenylene group).
 8. The radiationabsorbing polymer described in claim 7 which absorbs a predeterminedwavelength radiation, wherein R₁₅ represents an ethylene group.
 9. Theradiation absorbing polymer described in one of claims 1 to 8 whichabsorbs a predetermined wavelength radiation, wherein said recurringunit represented by the formula 2 is a recurring unit represented by thefollowing formula 6:

wherein R₄ and R₅ represent independently a hydrogen atom, an alkylgroup, a carboxyl group or other organic group, and Ar is a chromophorewhich has absorption at a predetermined wavelength radiation andrepresents one of substituted or non-substituted benzene ring, condensedring or heterocyclic ring groups bonded directly or through a linkagegroup to carbon atom consisting the main chain.
 10. The radiationabsorbing polymer described in one of claims 1 to 9, wherein saidrecurring unit represented by the formula 2 is a recurring unitrepresented by the following formula
 7.

wherein R₄ and R₅ represent independently a hydrogen atom, an alkylgroup, a carboxyl group or other organic group, X₂ represents O,S, NR₁₆or a straight, branched or cyclic alkylene group containing at least onecarbon atom, R₁₆ represents a hydrogen atom or a substituted ornon-substituted, phenyl group or cyclic, straight or branched alkylgroup and Ar₁ is a chromophore which has absorption at a predeterminedwavelength radiation and represents one of substituted ornon-substituted benzene ring, condensed ring or heterocyclic ring groupsbonded directly or through a linkage group to X₂.
 11. A composition forradiation absorbing coating which contains the radiation absorbingpolymer described in one of claims 1 to
 10. 12. A method of forming aradiation absorbing coating by applying the composition for radiationabsorbing coating described in claim 11 to a substrate and then bakingthe coated substrate to form a radiation absorbing coating.
 13. Aradiation absorbing coating formed by the method described in claim 12.14. The radiation absorbing coating described in claim 13, wherein saidradiation absorbing coating is an anti-reflective coating.